For me, Circuit Max and Cardio and Weights are "lightweight" workouts.
I find IMAX 2 "easier" than 1 because the music's more invigorating and Cathe has more variety within the blasts than in 1.
Boot Camp is a good, and fun, workout, but as fun as the cardio is, they're 1 minute segments that don't build cardio capacity as well as other workouts.
I'm torn between what I find the toughest between BM, MIC, and IMAX 1--I don't do them as much anymore since the Intensity Series came out, as its music is far more energizing, and the older workouts are not as inviting due to music/production values. Also, since I now have a 5 disc programmable DVD player, I do segments of IMAX1 mixed in with segments from IMAX2, CTX, Boot Camp, & C&W--now THAT'S tough!!!
Whatever Cathe workout you choose, you will get a great workout. Have fun with it!!